You surprise me here RL
Let's look at the big picture here. We KNOW for a fact there is intelligent life here on earth. Alien intelligence is completely speculative. Therefore, the first and most obvious place to look for answers is here on earth. Yes the technology appears to be way beyond anything publicly known. That doesn't mean humans are incapable of discovering it. Technological breakthroughs are not necessarily always incremental. Like I said before an Alien civilization that discovered us would likely be astounded and certainly would investigate us. That said, to not make humans the most probable source of this phenomenon is absurd.